Analog-digital converter, analog-digital conversion method, and imaging device

Abstract

An analog-digital converter that includes voltage acquisition circuitry that acquires a voltage value of an analog signal in a settling period, calculation circuitry that calculates a predicted convergence voltage value of the analog signal based on the voltage value of the acquired analog signal, reference signal generation circuitry that generates a ramp wave reference signal based on the predicted convergence voltage value, comparison circuitry that compares the voltage value of the analog signal with the ramp wave, measurement circuitry that measures a time period from a generation of the reference signal to a time before the voltage value of the analog signal intersects with the ramp wave of the reference signal, and addition circuitry that derives a convergence voltage value of the analog signal by adding a voltage value corresponding to the measured time period and a voltage value based on the predicted convergence voltage value.

The invention claimed is: 
     
       1. An analog-digital converter comprising:
 a voltage acquisition unit configured to acquire a voltage value of an analog signal in a settling period of the analog signal; 
 a calculation unit configured to calculate a predicted convergence voltage value of the analog signal on a basis of the voltage value of the analog signal acquired by the voltage acquisition unit; 
 a reference signal generation unit configured to generate a ramp wave reference signal on a basis of the predicted convergence voltage value calculated by the calculation unit; 
 a comparison unit configured to compare the voltage value of the analog signal with the ramp wave of the reference signal; 
 a measurement unit configured to measure a time period from a generation timing of the reference signal to a time before the voltage value of the analog signal intersects with the ramp wave of the reference signal; and 
 an addition unit configured to derive a convergence voltage value of the analog signal by adding a voltage value corresponding to the time period measured by the measurement unit and a voltage value based on the predicted convergence voltage value. 
 
     
     
       2. The analog-digital converter according to  claim 1 , wherein
 the reference signal generation unit maintains a first voltage value during the settling period of the analog signal, changes a voltage value at a first inclination to a voltage value based on the predicted convergence voltage value after the analog signal is converged, and then, generates a ramp wave that changes the voltage value at a second inclination smaller than the first inclination. 
 
     
     
       3. The analog-digital converter according to  claim 2 , wherein
 the voltage value based on the predicted convergence voltage value is a voltage value at which generation of the ramp wave that changes the voltage value at the second inclination is started. 
 
     
     
       4. The analog-digital converter according to  claim 1 , wherein
 the voltage acquisition unit compares the voltage value of the analog signal with the ramp wave in the settling period of the analog signal and acquires a voltage value of the analog signal when the ramp wave intersects. 
 
     
     
       5. The analog-digital converter according to  claim 4 , wherein
 the calculation unit calculates the predicted convergence voltage value of the analog signal by using the voltage value of the analog signal acquired by the voltage acquisition unit and a time period from start of settling of the analog signal to a time before the voltage value of the analog signal intersects with the ramp wave. 
 
     
     
       6. The analog-digital converter according to  claim 1 , wherein
 the calculation unit calculates the predicted convergence voltage value of the analog signal by using a fixed voltage that has been set in advance and a time period from start of settling of the analog signal to a time before the voltage value of the analog signal intersects with the fixed voltage. 
 
     
     
       7. An analog-digital conversion method for executing processing comprising:
 a step of acquiring a voltage value of an analog signal in a settling period of the analog signal and calculating a predicted convergence voltage value of the analog signal on a basis of the acquired voltage value of the analog signal; 
 a step of generating a ramp wave reference signal on a basis of the predicted convergence voltage value of the analog signal; 
 a step of measuring a time period from a generation timing of the ramp wave reference signal to a time before the voltage value of the analog pixel signal intersects with the ramp wave of the reference signal; and 
 a step of deriving a convergence voltage value of the analog signal by adding a voltage value corresponding to the measured time period and a voltage value based on the predicted convergence voltage value. 
 
     
     
       8. The analog-digital conversion method according to  claim 7 , wherein
 the voltage values of the analog signal are acquired a plurality of times at equal intervals in the settling period of the analog signal. 
 
     
     
       9. The analog-digital conversion method according to  claim 7 , wherein
 the voltage values of the analog signal are acquired a plurality of times at unequal intervals in the settling period of the analog signal. 
 
     
     
       10. The analog-digital conversion method according to  claim 7 , wherein
 a gain of an analog-digital converter is adjusted according to luminance information. 
 
     
     
       11. An imaging device comprising:
 a pixel array unit configured by arranging pixels including photoelectric conversion units in a matrix; and 
 an analog-digital converter configured to convert an analog pixel signal output from the pixel into a digital pixel signal, wherein 
 the analog-digital converter includes: 
 a voltage acquisition unit that acquires a voltage value of an analog signal in a settling period of the analog signal; 
 a calculation unit that calculates a predicted convergence voltage value of the analog signal on a basis of the voltage value of the analog signal acquired by the voltage acquisition unit; 
 a reference signal generation unit that generates a ramp wave reference signal on a basis of the predicted convergence voltage value calculated by the calculation unit; 
 a comparison unit that compares the voltage value of the analog signal with the ramp wave of the reference signal; 
 a measurement unit that measures a time period from a generation timing of the reference signal to a time before the voltage value of the analog signal intersects with the ramp wave of the reference signal; and 
 an addition unit that derives a convergence voltage value of the analog signal by adding a voltage value corresponding to the time period measured by the measurement unit and a voltage value based on the predicted convergence voltage value. 
 
     
     
       12. The imaging device according to  claim 11 , wherein
 pixel signal reading directions in an odd-number pixel column and an even-number pixel column are different from each other, and 
 the analog-digital converter is provided every other pixel column for each reading direction. 
 
     
     
       13. The imaging device according to  claim 12 , having a structure in which at least two semiconductor substrates including a first semiconductor substrate and a second semiconductor substrate are laminated, wherein
 a pixel array unit is formed on the first semiconductor substrate, and 
 the analog-digital converter is formed on the second semiconductor substrate.